Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 161050

Area Forecast Discussion
National Weather Service Wilmington NC
552 AM EST Tue Jan 16 2018

Weak high pressure will dissipate across the Carolinas today. A
cold front will move across the area Wednesday bringing a mix of
rain and snow with small accumulations possible inland. Cold and
dry arctic air will build into area Wednesday night and
Thursday. Temperatures should moderate over the weekend as high
pressure moves off the Southeast coast. Rain chances could
return Monday with the next cold front.


As of 300 AM Tuesday...A weakening ridge of high pressure extending
south into the Carolinas will hold on for most of the period. Warm
advection will occur above this surface-based layer allowing for
afternoon temperatures to top 50; much milder than yesterday but
still a few degrees below climatology. Moisture will increase in the
warm advection zone with clear skies this morning giving way to a
partly cloudy afternoon. The more pronounced increase increase in
moisture is slated to occur from west to east tonight as a cold
front approaches ahead of a strong trough and vorticity max. Some
very light rain or snow could begin affecting westernmost counties
by the end of the period. The ptype is a bit questionable as there
could be a late night minor rise in temperature.


As of 300 AM Tuesday...Virtually all 00Z model guidance is
showing more precipitation on Wednesday than was being shown 24
hours ago. The culprit appears to be a sharper mid and upper
level trough now being depicted moving across the area. This
leads to winds in the 850-500 mb layer backing by maybe 20
degrees compared to yesterday`s model runs, allowing the
northern Gulf of Mexico to be briefly tapped as a moisture
source and supplementing the meager Pacific moisture that is
being routed from the west. Where my QPF values were .02 to .04
yesterday, now a tenth of an inch or more is possible across
parts of the Sandhills.

Of course the bigger issue is how much of that QPF falls as
snow. The GFS is a cooler than the NAM with its low-level
thermal profiles which would allow for a more rapid changeover
to snow, particularly west of I-95 during the morning hours. The
new 00z ECMWF is a compromise solution between the GFS and NAM,
and implies rain should change to snow across Hartsville and
Bennettsville by 9 AM. Colder air aloft beneath the approaching
upper trough will continue to build eastward during the day,
offsetting any insolation trying to punch through the clouds and
allowing the changeover to occur in Lumberton by noon, and in
Elizabethtown and Whiteville by mid afternoon.

Given no warm nose aloft, this is likely to be a clean transition
from rain to snow without any sleet or freezing rain to deal
with. Forecast snowfall accumulations are up to 1 inch from
Bennettsville across northern Robeson and Bladen counties, with
less than half an inch from Darlington and Dillon to Lumberton
and Elizabethtown.

Precipitation is not likely to be as significant along the
coast as the Gulf of Mexico moisture connection is severed by
the time things get going here. Precip should end between 6-9 PM
along the coast, but even in Wilmington and Myrtle Beach there
could be a brief period of light snow at the tail end of the
event. Thinning moisture aloft should preclude any significant
snowfall totals here.

As skies clear and the core of the cold air aloft moves
overhead, lows Wednesday night should fall to 20-23, warmest
along the SC coast. Warm advection will begin on westerly
winds Thursday with clear, dry weather expected. Highs should
reach 40-45.


As of 300 PM Monday...Surface high building in from the west
Thu is quickly shifted east by zonal flow aloft. Lack of
troughing aloft coupled with quick eastward movement of the
surface high will limit duration of cold temps to Thu and Thu
night. Warm advection begins on Fri as the center of the high
slips south and then east of the area as Fri turns into Sat.
Southern stream shortwave moving across the Gulf of Mexico this
weekend opens up and weakens as it lifts northeast. By the time
it reaches the Southeast Sunday, the wave will have weakened
considerably. It may bring an increase in mid- level cloud cover
to the area but rainfall is unlikely. Best rainfall chances
during the period will be next week when a cold front, trailing
a surface low over the Great Lakes, moves into the region on
Mon. Still a lot of uncertainty, but there should be a period of
moisture return ahead of it, compliments of weak 5h ridging
over the weekend. The aforementioned 5h ridge coupled with low
level warm advection will produce temperatures 10 degrees above
climo during the later half of the period.


As of 12Z...VFR conditions will prevail through the forecast period.
A very weak pressure gradient will produce a light mainly northerly
wind today. Tonight, a cold front will approach the region from the
west. Only mid to high clouds expected at the end of the forecast
period. Any precipitation will be in the next set of TAFs.

Extended Outlook...Rain/MVFR/tempo IFR/with a chance for a
wintry mix Wed, otherwise VFR with high pressure in control.


As of 300 AM Tuesday...Light northerly winds today will be the
result of a ridge of high pressure extending south into the
Carolinas. As it weakens this ridge will progress eastward over
the coastline and winds may go light and variable early tonight.
Towards the end of the period a cold front will approach from
the west but its southerly winds appear to fail to overspread
the region during the near term. Winds will remain at 10kt or
less and may turn westerly.

As of 300 AM Tuesday...A cold front will move across the area on
Wednesday. While this won`t look like an impressive system on
the surface weather maps, it`s got plenty of cold air behind it
beneath a very powerful upper level system that will whip across
the area Wednesday night. Patchy rain Wednesday afternoon could
actually mix with or change to snow before ending Wednesday
night, particularly north of Cape Fear.

The biggest marine weather impact from this system is likely to
be increasing northwesterly winds behind the cold front,
anticipated to reach a solid 25 knots Wednesday night. Wind
chills could dip as low as 10-15 degrees on the beaches. This
will necessitate Small Craft Advisories which might be issued as
soon as this afternoon. Wind speeds should diminish during the
day Thursday.

As of 300 PM Monday...High pressure will pass south of the
waters Fri night into Sat. Gradient will remain weak Fri and Sat
with speeds 10 to 15 kt Fri diminishing to 10 kt or less Sat.
Seas trend down to 2 to 3 ft Fri and will remain 2 to 3 ft
through the end of the period.





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